Type Curves for Coalbed Methane Production Prediction

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCoalbed Methane (CBM) currently accounts for nearly 8 percent of U.S. annual gas production and approximately 12 percent of estimated total U.S. natural gas reserves. Coalbed methane proven reserves in the United States have increased from 3.7 Tcf in 1989 to 18.5 Tcf in 2002. This number is expected to increase even further as more resources are discovered and a better understanding of the existing resources is achieved. Appalachian Basin accounts about 10 percent of U.S. CBM resources. However, CBM production is very limited in the Appalachian Basin. The contribution of CBM to overall mix of natural gas sources in U.S. is expected to increase for next two decades. However, this cannot be achieved without substantial increase in CBM production in the Appalachian Basin. The problems causing the lag in development of CBM in the Appalachian Basin need to be overcome for CBM to reach its true potential in the U.S. energy equation.Gas production from CBM reservoirs is governed by complex interaction of single-phase gas diffusion through micro-pore system (primary porosity) and two-phase gas and water flow through cleat system (secondary porosity) that are coupled through desorption process. In order to effectively evaluate CBM resources, it necessary to utilize reservoir models that incorporate the unique flow and storage characteristics of CBM reservoirs. These models are often complicated to use, expensive, and time consuming. The typical gas producers in the Appalachian Basin suffer from the lack of scientific, userfriendly tools that can assist them in development of CBM resources. Therefore, it is necessary to develop tools that make it possible for typical (small to medium size) producers to seriously consider this important resource.This study presents a set of production type curves that would help the producers to predict the production from their CBM wells. As a consequence, the producers would be able to make better, more informed decisions regarding the CBM resources in the region. A reservoir model that incorporates the unique flow and storage characteristics of Coalbed Methane reservoirs was employed in this study to develop the type curves. The type curves provide a reliable tool to predict the production performance of CBM reservoirs both during dewatering and stable gas production phases. The application and issues concerning the production performance of CBM reservoirs are also discussed.

Production Data Analysis of CBM Wells

“…Unique type-curve sets are required for differing degrees of drawdown and initial water saturations. Aminian et al [14][15] also generated type-curves using a numerical simulator, and defined a new set of dimensionless variables. The type-curves were demonstrated to be sensitive to isotherm parameter assumptions, flowing pressure and relative permeability.…”

Developing synthetic reservoir type curve model for use in evaluating surface facility and gathering pipe network designs

“…The uncertainty in CBM wells is partly due to a complex production mechanism involving desorption of gas from the coal matrix and diffusion through the fractures and cleats under two-phase flow conditions (Aminian, et al, 2004). The mechanism of methane desorbing from the coal matrix through the cleats and fractures of the coal seam provides a challenge to correctly predict the time to peak, the magnitude of the peak as well as decline rate for both the gas and water phase accurately throughout the lifecycle of the field .…”

“…Fundamentally, type curves are pre-plotted solutions to the [reservoir] flow equations, such as the diffusivity equation, for selected types of formations and selected initial and boundary conditions (Lake & Fanchi, 2006). Type curves, showing either flow rate over time or cumulative production over time is a common tool used to describe the performance of a reservoir in unconventional gas well (Nobakht, et al, 2013;Mingqiang, et al, 2016;Sugiarto, et al, 2015;Burgoyne & Clements, 2014;Aminian, et al, 2004;Baihly, et al, 2010;Karacan, 2013;Mavor, et al, 2003).…”

Teste drawdown em um reservatório de coalbed methane

“…O comportamento da produção do coalbed é complexo e difícil de predizer e analisar (Aminian et al, 2004) já que é controlado por uma interação complexa entre a matriz de carvão e o fluxo bifásico de gás e água (Aminian et al, 2007). Diversos fatores podem afetar a produtividade de um reservatório de CBM, tais como a quantidade de gás presente, a litologia do carvão, a hidrodinâmica e saturação do reservatório e a permeabilidade.…”